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Shutemov" Cc: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH] mm/gup: disallow GUP writing to file-backed mappings by default Message-ID: References: <20230424120247.k7cjmncmov32yv5r@box.shutemov.name> <3273f5f3-65d9-4366-9424-c688264992f9@lucifer.local> <20230424134026.di6nf2an3a2g63a6@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230424134026.di6nf2an3a2g63a6@box.shutemov.name> X-Rspam-User: X-Rspamd-Queue-Id: 8DF77A002F X-Rspamd-Server: rspam01 X-Stat-Signature: 9kyhk66sbrfa5333eb9517qtmf48mhgy X-HE-Tag: 1682359208-831731 X-HE-Meta: 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 V0GoT6aI 0DtSbxVdT5O8jkHf6Ji5Qt2a64+naiBuhmzuWeXh+6ej3Ad04uhPivVRkMSIvUJ3YHoZBiR8WrdbaHFYISCG9X26FcmggjJnfRRfyWr34Wjc5XkKcCR57CM3jPWP5oZP1NQ4J7BALW+Q03d90puGop2PMuFWZCAZ9mw27ngY89pFUvRXITxxPGiYsVXhhn9ALWqy2M+QUPB2K8GRFimN35qFhpqU1cnJ/+Xq8efryi+I7vnjbqbnEcrs9oFihcAa8IeMF6efCBLkJc6PB3/XAnZdszdMBoce42WDR9rTmQ8MiNwJ6YYd5gNIT2XRL6jNr3fm76imlR5JtmE4Ke9mOFVRY1GIZz3f1juc7JMTy8k0JGSr1z5MwJ96ds80rYZngCcY4p/WtmB0NN38= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Apr 24, 2023 at 04:40:26PM +0300, Kirill A. Shutemov wrote: > > Something more general would be preferable, however I believe there were > > concerns broader than write notify, for instance not correctly marking the > > folio dirty after writing to it, though arguably the caller should > > certainly be ensuring that (and in many cases, do). > > It doesn't make much sense to me. > > Shared writable mapping without page_mkwrite (or pfn_write) will setup > writeable PTE even on read faults[1], so you will not get the page dirty, > unless you scan page table entries for dirty bit. The general statement for supporting GUP is that the VMA owner never relies on write protect, either explicitly through removing the write bit in the PTE or implicitly through zapping the inode and removing all PTEs. The general bug we have is that the FS does some action to prevent writes and then becomes surprised that the page was made dirty. GUP allows write access to the page to continue past any write protect action the FS takes. AFAIK all GUP users do correctly do mkdirty and we have helpers to support this during unpin, that is not the bug. So, I don't know about page_mkwrite, if it correlates with the abvoe then great :) Jason